Exhaust heat recovery for engine heating and exhaust cooling

ABSTRACT

Various systems and method for heating an engine in a vehicle are described. In one example, intake air flowing in a first direction may be heated via a gas-to-gas heat exchange with exhaust gases. The heated intake air may then be used in a subsequent gas-to-liquid heat exchange to heat a fluid circulating through the engine. In another example, intake air flowing in a second direction may be heated via a heat exchange with exhaust gases in order to cool an exhaust catalyst.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/345,005, entitled “EXHAUST HEAT RECOVERY FOR ENGINE HEATINGAND EXHAUST COOLING,” filed on Jan. 6, 2012, which is a continuation ofU.S. patent application Ser. No. 12/793,447, entitled “EXHAUST HEATRECOVERY FOR ENGINE HEATING AND EXHAUST COOLING,” filed on Jun. 3, 2010,now U.S. Pat. No. 8,091,359, the entire contents of each of which arehereby incorporated by reference for all purposes.

TECHNICAL FIELD

The present application relates to heat exchange and, more specifically,to using a heat exchanger for engine heating and exhaust cooling.

BACKGROUND AND SUMMARY

Under cold start conditions, an engine has cooled to ambient conditions,which may be relatively hot or cold, and each component of the enginewarms-up to a desired operating temperature. During this time, emissionsmay be higher and there may be energy losses such as viscous energylosses due to a relatively cool temperature of fluids (e.g., engine oil,transmission fluid, etc.) circulating through the powertrain.

Some methods for expediting engine heating include exhaust heatrecovery. In some examples, exhaust heat is transferred to enginecoolant, for example, via a heat exchanger. Such a method, however, maybe only marginally effective in quickly heating the combustion chamberand/or reducing fluid viscosity.

The inventors herein have recognized the above problems and have devisedan approach to at least partially address them. Thus, a method forheating an engine in a vehicle is disclosed. The method comprisesheating intake air via a gas-to-gas heat exchanger, the gas-to-gas heatexchanger in communication with exhaust gases, and heating a fluid whichflows through the engine with the intake air via a gas-to-liquid heatexchanger.

By heating intake air with exhaust heat and then transferring some ofthe heat to a powertrain fluid such as engine oil, the fluid may beheated thereby reducing energy losses due to the viscosity of the fluidin addition to reducing combustion chamber heat loss. Further, theheated intake air may be cooled via the heat exchange with thepowertrain fluid, yet still be warmer than ambient air such that enginepumping losses may also be reduced, but not so hot that combustionstability is reduced or knock instigated. Further, during warmed-up orboosted operating conditions, for example, heated intake air may causeknock under some conditions; however, during a cold start with theengine warming up, the possibility of the heated intake air causingknock is decreased. As such, a synergistic operation may be achieved.

Another advantage of the disclosed approach is the warming of the enginecoolant with air that has picked up heat from the exhaust can increasethe heat available for cabin warming. Further, engines often have oilcoolers to mitigate peak oil temperatures for engine used at extremeconditions. Thus, the disclosed approach uses the air-to-oil (e.g.,gas-to-liquid) heat exchange to achieve oil cooling by reversing theairflow direction via the increased boost, which occurs precisely attimes when engine oil cooling needs arise.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of an engine including a gas-to-gas heatexchanger and a gas-to-liquid heat exchanger.

FIG. 2 shows a flow chart illustrating a routine for heating an engine.

FIG. 3 shows a flow chart illustrating a routine for cooling an exhaustcatalyst and/or powertrain fluid.

DETAILED DESCRIPTION

The following description relates to systems and methods for heating anengine in a vehicle during a cold start. In one example, intake airflowing in a first direction may be heated through a heat exchange withexhaust gas via a gas-to-gas heat exchanger. The heated intake air maysubsequently undergo a second heat exchange with a powertrain fluid(e.g., engine oil, transmission fluid, etc.) via a gas-to-liquid heatexchanger such that the powertrain fluid is heated. As such, viscousenergy losses due to relatively cold fluid may be reduced, andcombustion chamber heat loss and pumping losses are also reduced due tothe heated intake air. Furthermore, in another example, when pumpingloss reduction and powertrain fluid heating are not desired, but exhaustcooling is desired, intake air may flow through the heat exchangers in asecond direction such that the exhaust is cooled for exhaust catalystcooling, for example.

FIG. 1 shows a schematic diagram of vehicle system 100. Vehicle system100 includes engine 10 which may be included in a propulsion system ofan automobile, engine 10 having a plurality of cylinders 30. Engine 10may be controlled at least partially by a control system 14 includingcontroller 12 and by input from a vehicle operator via an input device(not shown in FIGS. 1 and 2). Vehicle system 100 includes exhaustmanifold 48 leading to exhaust passage 50 which eventually leads to atailpipe (not shown in FIG. 1) that eventually routes exhaust gas to theatmosphere. As described in more detail below, exhaust passage 50 ofvehicle system 100 may include one or more emission control devices.

Vehicle system 100 further includes control system 14. Control system 14is shown receiving information from a plurality of sensors 16 (variousexamples of which are described herein) and sending control signals to aplurality of actuators 81 (various examples of which are describedherein). As one example, sensors 16 may include manifold air pressure(MAP) sensor 24 located in intake manifold 44. Additionally, othersensors such as temperature, air-fuel ratio, and composition sensors maybe coupled to various locations in vehicle system 100. As anotherexample, the actuators may include actuators for fuel injectors (notshown), throttle 20, air bypass valve 22, and other control valves thatare not shown in FIG. 1. As shown in FIG. 1, air bypass valve 22provides a source of warm, non-dilute air to engine 10. Throttle 20provides a source of cool air to engine 10 which may be diluted withEGR, for example. Further, air bypass valve 22 can be used totransiently provide non-dilute air if EGR is metered upstream of thispoint.

Vehicle system 100 further includes charge air cooler (CAC) 60. CAC 60is arranged along the intake passage upstream of throttle 20 for coolingthe engine intake air after it has passed through the turbochargerand/or if it is diluted with EGR, for example. Further, air filter 38 isshown arranged along the intake passage upstream of CAC 60. For example,air filter 38 may remove particulates from the intake air.

Control system 14 includes controller 12. Controller 12 may be amicrocomputer including the following, although not shown in FIG. 1: amicroprocessor unit, input/output ports, an electronic storage mediumfor executable programs and calibration values (e.g., a read only memorychip), random access memory, keep alive memory, and a data bus. Storagemedium read-only memory may be programmed with computer readable datarepresenting instructions executable by the microprocessor forperforming the methods described below as well as other variants thatare anticipated but not specifically listed. For example, the controllermay receive communication (e.g., input data) from the various sensors,process the input data, and trigger the actuators in response to theprocessed input data based on instruction or code programmed thereincorresponding to one or more routines. Example routines are describedherein with reference to FIGS. 2 and 3.

Engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 52 arrangedalong an intake passage. For a turbocharger, compressor 52 may be atleast partially driven by turbine 54 via a shaft (not shown) arrangedalong the exhaust passage. For a supercharger, compressor 52 may be atleast partially driven by the engine and/or an electric machine, and maynot include a turbine. Thus, the amount of compression provided to oneor more cylinders of the engine via a turbocharger or supercharger maybe varied by controller 12. Further, vehicle system 100 includescompressor bypass valve (CBV) 53 to release pressure in the intakesystem when the engine is boosted. In some embodiments (not shown), airflowing in a first direction through air bypass valve 22 may join theintake passage upstream of throttle 20. In such an embodiment, airbypass valve 22 may also be used as a compressor bypass valve. Wastegate55 is provided to divert exhaust gases to regulate the speed of turbine54, for example.

Engine 10 is shown coupled to exhaust passage 50 upstream of emissioncontrol devices 70 and 71 in FIG. 1. As an example, emission controldevices 70 and 71 may be a three way catalyst (TWC), NO_(x) trap,particulate filter, selective catalyst reduction (SCR) system, variousother emission control devices, or combinations thereof. In someembodiments, during operation of engine 10, emission control devices 70and/or 71 may be periodically reset by operating at least one cylinderof the engine within a particular air/fuel ratio.

Further, as shown in the example embodiment of FIG. 1, vehicle system100 further includes heat exchangers 34 and 36. Heat exchanger 34 may bea gas-to-gas heat exchanger for heating intake air and cooling exhaustgas. Heat exchanger 36 may be a gas-to-liquid heat exchanger forexchanging heat between intake air and a fluid circulating through thepowertrain such as engine oil, transmission fluid, coolant, etc. Theliquid flow through heat exchanger 36 may optionally be shut off viavalve 37 to get very hot air to the intake manifold, if desired. In someembodiments, the exhaust heat can be removed at any point along theexhaust conduit, even as far upstream as to cool the exhaust port orexhaust manifold. For example, heat exchanger 34 may be positioned atvarious locations along the exhaust conduit, not just between emissioncontrol devices 70 and 71 as shown in FIG. 1. As an example, heatexchanger 34 may be positioned upstream of emission control device 70.

In the example embodiment of FIG. 1, intake air may flow in a firstdirection through air bypass valve 22. During periods when air bypassvalve 22 is open and the engine is not boosted (as will be described infurther detail below), intake air may be drawn through air bypass valve22 such that it first flows through heat exchanger 34. As such, intakeair flowing through heat exchanger 34 is heated while the exhaust gasflowing through heat exchanger 34 is cooled. Heated intake air may bedesired, for example, to reduce pumping losses at part load. Heatedintake air leaving heat exchanger 34 then enters heat exchanger 36 whereheat exchange occurs between the intake air and a powertrain fluid.During a cold engine start, for example, heat from the heated intake airis transferred to the powertrain fluid and the temperature of the fluidincreases, which may be desired to reduce viscous friction losses.Further, the temperature of the heated intake air that is delivered tothe engine is reduced during the heat exchange resulting in an airtemperature that is not too hot for engine intake use, for example.Vehicle system 100 may also include check valve 76 (depicted along adashed line in FIG. 1) upstream of heat exchanger 36 in order to ventsome of the hot air when less heating of the powertrain fluid is desiredor if less cooling of the exhaust catalyst is desired during powertrainfluid cooling, for example.

Further, in the example embodiment of FIG. 1, intake air may flow in asecond direction through air bypass valve 22. During periods when theengine is boosted (e.g., the turbocharger is in operation and manifoldair pressure is greater than barometric pressure), some excess intakeair may flow through air bypass valve 22 to heat exchanger 36. As such,some cooling of the powertrain fluid occurs. In some embodiments, thepowertrain fluid system may have a valve (e.g., valve 37) that, whenclosed, can cease flow of the fluid through heat exchanger 36, ifdesired. In such an embodiment, no heat exchange takes place when theexcess intake air passes through the heat exchanger 36. After flowingthrough heat exchanger 36, the excess intake air passes through heatexchanger 34. As such, exhaust gas passing through heat exchanger 34 iscooled which may facilitate catalyst cooling. Further, in such anembodiment, the intake air is heated as it passes through heat exchanger34. As such, vehicle system 100 includes check valve 78 to prevent thehot intake air from re-entering the intake passage. Vehicle system 100further includes check valve 77 to allow the hot air to be vented to theatmosphere.

As illustrated in the embodiment of FIG. 1, vehicle system 100 furtherincludes venturi 45 coupled to check valve 75. The flow of air in eitherdirection through venturi 45 may be used a vacuum source. As an example,the vacuum generated via venturi 45 may be used for the brake system(not shown).

The flow charts in FIGS. 2 and 3 illustrate control routines forcontrolling airflow through an air bypass valve, such as air bypassvalve 22 described above, in the directions depicted in FIG. 1 and maybe used together and carried out in a coordinated way.

FIG. 2 shows a flow chart illustrating a control routine 200 for heatingan engine in a vehicle, such as engine 10 described above with referenceto FIG. 1. Specifically, routine 200 determines engine operatingconditions and opens the air bypass valve to allow intake air to flowthrough in a first direction based on the operating conditions.

At 210 of routine 200, engine operating conditions are determined.Engine operating conditions may include engine temperature, boost level,powertrain fluid temperature, etc.

Once the engine operating conditions are determined, routine 200proceeds to 212 where it is determined if the engine is under a coldstart. As referred to herein, “cold start” implies the engine is startedunder conditions in which the engine has cooled to ambient conditions,which may be relatively hot or cold. If the engine is not under coldstart conditions, routine 200 moves to 226 where current engineoperation is continued and the routine ends. For example, the currentengine operation may include operating with the air bypass valve closedand air-fuel control not accounting for variation in intake charge dueto either direction of airflow in the air bypass valve.

On the other hand, if it is determined that the engine is under coldstart conditions, routine 200 continues to 214 where it is determined ifthe turbocharger is on. In some embodiments, for example, theturbocharger may have a bypass valve (e.g., a wastegate) that directsflow around the turbine such that the intake air is not boosted. Assuch, the valve may be positioned such that a minimum level of exhaustgas flows through the turbine when boosted intake air is not desired. Ifit is determined that the turbocharger is on and intake air is boostedabove a threshold level (e.g., if boost pressure (intake manifoldpressure) is greater than atmospheric pressure), routine 200 moves to226 where current engine operation is continued and the routine ends.

If it is determined that the turbocharger is not in operation (e.g., thewastegate is open), routine 200 of FIG. 2 proceeds to 216 where the airbypass valve is opened. The air bypass valve may be a butterfly valve,for example, that can be adjusted to regulate the flow of intake airthrough the valve. The opening of the valve may be based on variousoperating parameters, and once the air bypass valve is open, routine 200continues to 218 where the openings of the air bypass valve and throttleare adjusted based on a desired amount of heating of the intake airand/or powertrain fluid, such as engine oil. For example, the throttlemay be completely closed such that only heated intake air enters theengine. As another example, the air bypass valve may be completelyopened such that a maximum amount of intake air is drawn through thegas-to-liquid heat exchanger for heating a powertrain fluid and thethrottle may be partially open to allow cooler air to enter thecylinders of the engine. Further, the amount of bypass air flowing maybe adjusted responsive to engine coolant temperature in an inverseproportion.

Further, in some embodiments, an amount of powertrain fluid flowingthrough the gas-to-liquid heat exchanger may be adjusted via a valve inthe powertrain fluid system, for example, such that a desired amount ofintake air heating is achieved. For example, increased fluid flow may beprovided when bypass air temperature is high, to increase fluid heatingand moderate bypass air temperature to prevent damage to intakemanifold, fuel injectors, etc.

After the openings of the throttle and air bypass valve are adjusted,routine 200 continues to 220 where air-fuel ratio control is adjusted.For example, varying amounts of air entering the intake manifold throughthe throttle and the air bypass valve can change the pressure detectedby the MAP sensor as well as an amount of air entering the cylinders ofthe engine, for example. As such, fuel injection may be adjusted in anopen loop manner from the MAP sensor, based on a direction of bypassflow, and an amount of bypass flow, to maintain a desired air-fuelratio, for example. In one example, when bypass flow is present, andopen loop fuel injection adjustment is provided increasing open loopfuel injection when bypass flow enters the intake manifold, decreasingopen loop fuel injection when bypass flow exits the intake manifold, andno additional open loop fuel injection adjustment with there is nobypass flow

At 222 of routine 200, it is determined if conditions are met forcompletion of powertrain warm-up. Conditions for completion ofpowertrain warm-up may include engine temperature greater than athreshold temperature, fluid temperature greater than a thresholdtemperature, time since start, etc. If one or more of the conditions forpowertrain warm-up are not met, routine 200 continues until theconditions are met.

Once the conditions for completion of powertrain warm-up are met,routine 200 continues to 224 where the throttle and the air bypass valveare adjusted to optimize engine efficiency based on pumping work andknock. For example, if the increased temperature of intake air begins tocause knock in one or more engine cylinders, the bypass valve may bepartially or fully closed so that the temperature in the cylinders isdecreased and knock is reduced. If the temperature of the intake airexceeds a threshold temperature (e.g., a maximum temperature), the airbypass valve may be partially or fully closed (and the throttle openingmay be increased) to prevent damage to fuel injectors, intake manifold,etc. If the pressure of the intake manifold exceeds a threshold pressure(e.g., 90 kPa), the air bypass valve may be partially or fully closed(and the throttle opening may be increased) to ensure that the enginecan produce the desired torque without boosting. If none of theseconditions is met, the air bypass may be partially or fully opened (andthe throttle opening may be decreased) to increase intake airtemperature, reduce intake air density, reduce engine pumping losses,and improve engine efficiency.

Thus, the air bypass valve may be controlled to allow intake air to flowthrough a series of heat exchangers in order to heat engine intake airas well as a powertrain fluid. In this manner, fuel economy may beincreased as intake stroke pumping work is decreased due to theincreased intake charge temperature. Further, heating of powertrainfluid circulating through the engine such as oil or transmission fluidto a desired temperature for warmed-up engine operation may be expeditedthereby reducing viscous energy losses due to friction.

Continuing to FIG. 3, which may be used in combination with FIG. 2, aflow chart illustrating a control routine 300 for cooling an exhaustcatalyst, such as exhaust catalyst 71 described above with reference toFIG. 1, and/or cooling powertrain fluid is shown. Specifically, routine300 determines engine operating conditions and opens the air bypassvalve to allow intake air to flow through in a second direction (e.g.,the reverse of the first direction) based on the operating conditions.

At 310 of routine 300, engine operating conditions are determined. Asdescribed above, engine operating conditions may include exhaustcatalyst temperature, manifold air pressure, boost level, etc.

Once the engine operating conditions are determined, routine 300proceeds to 312 where it is determined if catalyst and/or fluid coolingare desired. For example, the catalyst may be a particulate filter thatis periodically regenerated at high temperature, and it may be indicatedthat catalyst cooling is desired after particulate filter regenerationor if the catalyst temperature increases above a threshold temperatureduring regeneration, for example. As another example, during conditionsin which the engine is boosted, the powertrain fluid temperature mayincrease above a desired temperature and fluid cooling may be desired.

If it is determined that catalyst and/or fluid cooling is not desired,routine 300 moves to 324 where current engine operation is continued andthe routine ends. On the other hand, if it is determined that catalystand/or fluid cooling is desired, routine 300 continues to 314 where isit determined if the turbocharger is on (e.g., the engine is boosted).If it is determined that the engine is not boosted, routine 300 moves to326 where the turbocharger is turned on in order to boost the engine.

If it is determined that the turbocharger is on (e.g., boost pressure isgreater than a threshold value) at 314 or once the turbocharger isturned on (e.g., the wastegate is at least partially closed) at 326,routine 300 proceeds to 316 where the air bypass valve is opened. Insome embodiments, for example, the air bypass valve may be opened oncethe air pressure in the intake manifold (MAP) increases above thebarometric pressure.

As described above, the opening of the air bypass valve may beadjustable such that the flow of intake air through the air bypass valvemay be regulated. Further, openings of the throttle and air bypass valvemay be adjusted in order to achieve a desired amount of flow through thegas-to-gas heat exchanger.

Further, if powertrain fluid cooling is desired, a valve (e.g., valve 37described above with reference to FIG. 1) may be opened to allow fluidto flow through the gas-to-liquid heat exchanger. On the other hand, ifpowertrain fluid cooling is not desired, the valve may be closed suchthat heat from the fluid is not lost to the intake air during catalystcooling.

Once the air bypass valve is opened at 316, routine 300 proceeds to 318and air-fuel ratio control is adjusted. In this example, a varyingamount of air leaves the intake manifold through the air bypass valve.As such, open loop feedback based on the MAP sensor, for example, mayindicate a smaller amount of fuel injection in order to maintain adesired air-fuel ratio, as discussed herein.

At 320 of routine 300, it is determined if the exhaust catalyst and/orthe powertrain fluid has reached the desired temperature. Thetemperature may be measured by a temperature sensor coupled to thecatalyst or within the powertrain fluid circuit, for example. In someexamples, the desired temperature may be a warmed-up operatingtemperature of the catalyst. In other examples, the desired temperaturemay be a temperature of the catalyst required for regeneration.

If the catalyst has not reached the desired temperature, routine 300returns to 320 until the catalyst has reached the desired temperature.Once it is determined at 320 that the desired temperature has beenreached, routine 300 continues to 322 where the air bypass valve isclosed and air-fuel ratio control is adjusted. As such, intake air nolonger flows through the series of heat exchangers. Further, when theair bypass valve is closed, air enters the intake manifold only throughthe throttle and air no longer leaves the intake manifold through theair bypass valve. Thus, fuel injection may be adjust based on open loopfeedback from the MAP sensor, for example.

Thus, the air bypass valve may be controlled to allow intake air to flowthrough a series of heat exchangers in order to cool exhaust gas and anexhaust catalyst, and/or powertrain fluid. In this manner, cooling ofexhaust gas and the exhaust catalyst with fuel enrichment may bereduced, for example.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application.

Such claims, whether broader, narrower, equal, or different in scope tothe original claims, also are regarded as included within the subjectmatter of the present disclosure.

1. A method for a vehicle engine, comprising: heating intake air drawn from upstream of a turbocharger via a gas-to-gas heat exchanger, the gas-to-gas heat exchanger in communication with exhaust gases; and then heating a fluid with the heated intake air via a gas-to-liquid heat exchanger, the fluid flowing through the engine.
 2. The method of claim 1, wherein the fluid is at least one of engine oil, engine coolant, or transmission oil.
 3. The method of claim 1, wherein an amount of the heated intake air is adjusted via an air bypass valve.
 4. The method of claim 1, further comprising heating the intake air and the fluid during a cold engine start.
 5. The method of claim 1, further comprising heating the intake air during warmed-up operation.
 6. The method of claim 1, wherein the gas-to-gas heat exchanger is positioned upstream of an exhaust catalyst.
 7. The method of claim 6, further comprising cooling the exhaust catalyst when the turbocharger is in operation and boost is greater than a threshold value.
 8. The method of claim 1, further comprising adjusting a valve to reduce a flow of the fluid through the gas-to-liquid heat exchanger when a temperature of the fluid is greater than a threshold temperature.
 9. A method for an engine in a vehicle, the engine having a turbocharger and an exhaust catalyst, comprising: heating intake air drawn from upstream of the turbocharger via a gas-to-gas heat exchanger, the gas-to-gas heat exchanger in communication with exhaust gases; then passing the heated intake air through a gas-to-liquid heat exchanger to heat a fluid that flows through the engine and to reduce a temperature of the heated intake air; and then delivering the heated intake air to a cylinder of the engine via an air bypass valve.
 10. The method of claim 9, wherein the gas-to-gas heat exchanger is positioned upstream of an exhaust catalyst.
 11. The method of claim 10, further comprising cooling the exhaust catalyst or engine fluid when the turbocharger is in operation and boost is greater than a threshold value.
 12. The method of claim 9, wherein the fluid is at least one of engine oil, engine coolant, or transmission oil.
 13. The method of claim 9, wherein the method is carried out under cold start conditions when the turbocharger is not in operation.
 14. The method of claim 9, further comprising adjusting the air bypass valve to adjust an amount of heated intake air delivered to the engine.
 15. The method of claim 9, further comprising closing the air bypass valve when a temperature of the fluid is greater than a threshold temperature.
 16. A system, comprising: an engine with an intake passage through which intake air flows and an exhaust passage through which exhaust gas flows; a turbocharger; a throttle disposed downstream of the turbocharger in the intake passage; an air bypass valve; a gas-to-gas heat exchanger in communication with the intake air and the exhaust gas; a gas-to-liquid heat exchanger in communication with intake air and a fluid circulating through the engine; and a controller configured to identify an operating condition, and based on the operating condition, adjust openings of the throttle and air bypass valve such that intake air drawn from upstream of the turbocharger flows in a first direction through the gas-to-gas heat exchanger and then through the gas-to-liquid heat exchanger and heated intake air enters a cylinder of the engine.
 17. The system of claim 16, wherein the operating condition includes cold engine start while the turbocharger is not in operation.
 18. The system of claim 16, wherein the operating condition includes a temperature of the fluid circulating through the engine and a boost pressure, and the controller is further configured to close the air bypass valve responsive to a temperature of the fluid less than a threshold temperature when the boost pressure is greater than a threshold value.
 19. The system of claim 16, wherein the system further includes an exhaust catalyst disposed downstream of the gas-to-gas heat exchanger.
 20. The system of claim 19, wherein, responsive to boost greater than a threshold value when the turbocharger is in operation, the controller is further configured to adjust the openings of the throttle and air bypass valve such that intake air drawn from downstream of the turbocharger flows in a second direction through the air bypass valve, the second direction being a reverse of the first direction, and the exhaust catalyst is cooled. 